1. Field of the Invention
The present invention relates generally to an electron gun for a color CRT (Cathode-ray tube) having three cathodes disposed in parallel to each other. Particularly the present invention relates to a technique for preventing a halo phenomenon occurring on an electron beam of a CRT screen.
2. Description of the Prior Art
Generally, electron guns utilized in color CRTs utilize, for example, three cathodes, electrodes for forming a specified electric field, and a convergence deflector. The side beams of the three electron beams produced by the cathodes are converged once, disperse, and then enter the convergence deflector where the side beams are again deflected, the three beams then being focused to converge at a single point on the CRT screen.
For such three cathode electron guns, an arrangement wherein the three cathodes are disposed in parallel has been widely adopted as such an arrangement is easily constructed.
However, such parallel-cathode type electron guns have a drawback in that an astigmatic lens effect is subjected to the side beams since the side beams need to be greatly deflected. Such astigmatic lens effect causes an asymmetric halo on the CRT screen which, if left uncorrected, deteriorates the focusing characteristics of the CRT.
It has been proposed to compensate for such an astigmatic lens effect by providing a counter-astigmatic lens effect for neutralizing the negative effects on the side beams. However, provision of such a counter-astigmatic lens effect tends to deteriorate focusing characteristics of the central beam and the CRT quality is degraded.
Thus, it has been required to provide an electron gun for a color CRT having parallel-cathode construction which can eliminate a halo effect from occurring on the CRT screen and and in which optimal focusing characteristics are maintained.